Directions

MIX the mustard in a bowl with salt and pepper. Cover and let sit at room temperature at least 30 minutes to allow the flavours to meld.
REMOVE the turkey from the refrigerator 1 hour before roasting. Preheat the oven to 325 degrees F. Rub the outside of the turkey with the butter and season liberally with salt and pepper. Put 4 cups poultry stock in a medium saucepan and keep warm over low heat.
PLACE the carrots, celery, onions, and fennel in a large roasting pan and place the turkey on top.
PLACE in the oven and roast, basting with the warm stock every 30 minutes until an internal thermometer registers 155 degrees F.
BEGIN basting with the mustard glaze; continue roasting, basting with the glaze every 10 minutes, until an instant-read thermometer reaches 165 degrees F, about 20 more minutes.
REMOVE the turkey from the oven. Tent loosely with foil and let rest at least 45 minutes before slicing.
SERVE with roasted vegetables and spoon drippings over the top.